Well, after a certain point the proliferation of subforums just results in difficult navigation. While people familiar with the site may find it useful (I don't know, I'm not one of them) I'm inclined to think the proliferation of (largely meaningless) choices will just confuse newcomers and end up causing a lot of trouble for little benefit.

Personally, I browse from the front page (or one of the "recent activity" searches), so I don't pay any attention at all to the subforums, but keeping the divisions down to a minimum reduces confusion and prevents irritating fragmentation.